Hot water heaters are well known devices for heating cold water. These devices typically consist of an insulated tank which stores cold water to be heated. The water is typically heated electrically or by combusting gas at the base of the tank and allowing the exhaust to flow up through the a series of internal pipes and out an exhaust port. The cold water within the tank is heated either as a result of being in contact with the electrical coil or the internal pipes which carry the combusted gasses. The major drawback of such hot water heating systems, however, is the excessive operating costs.
One way to reduce the operating costs of a hot water heating system is to increase the efficiency of the system. In thermodynamics terms, efficiency is the ratio of useful energy output by a system compared to the total energy input to the system. The efficiency of a hot water heating system, therefore, is effectively the ratio of the temperature increase of the water therein, compared to the fuel energy spent to achieve that increase. Thus, assuming the volume of water remains constant, an improvement in the efficiency of a hot water heating system will result in a reduction in the amount of energy required to heat the water to a given temperature. This is because the system will require less energy to produce the same result as compared to a less efficient system.
Alternatively, one can improve the operating costs of a hot water heating system by utilizing a cost free energy source. In this scenario the efficiency of the hot water heating system remains unchanged, as the system itself is unchanged. As a result of using a cost free energy source, however, one reduces the total amount of energy required to heat the water. As a result, a reduction in operating costs also occurs.
Several prior art attempts have been made to reduce operating costs of hot water heating systems by improving efficiency. Typically, these prior art systems recycle energy produced for the purpose of heating the water therein. Such increases in efficiency are typically achieved through the use of a pre-heating device often referred to as a pre-heater.
One example of a hot water pre-heating device is a flue exhaust pre-heater. In order to pre-heat incoming cold water, flue exhaust pre-heaters utilize heated gasses exhausted from the hot water heating process. The pre-heating of the water is achieved by directing the flow of exhaust fumes across the incoming cold water pipes, prior to entry of these pipes into the hot water tank. Thus, by utilizing energy that is otherwise lost to atmosphere, the efficiency of the hot water heating system may be increased. This is because the amount of energy required to produce the desired result may be reduced. An example of such a pre-heater is shown in U.S. Pat. No. 4,175,518 to Reames, Jr. The major drawback of such a system, however, is the complex modifications that must be made to one's existing heating system, to utilize the pre-heater. For example, one must not only modify the existing exhaust means of the hot water heater, but also the cold water delivery pipes. With respect to the cold water pipes, this may be an onerous task as the pipes are often wound into a coil or other complex shape which maximizes heat transfer. Furthermore, such a device cannot be used in an electrical hot water heating system, as the pre-heater described above is reliant on heated exhaust for operation.
Other prior art pre-heaters recycle exhaust fumes from other sources as an attempt to reduce the operating costs of a hot water heating system. For example, U.S. Pat. No. 4,484,564 to Erickson discloses a system wherein the exhaust from one's chimney is used to pre-heat incoming cold water. The pre-heating which occurs in this system is the result of placing the cold water delivery pipes within a residential chimney. Similar to the flue-exhaust pre-heater, however, use of this system requires complex modifications to one's pre-existing hot water heating system. Furthermore, as will be apparent to one skilled in the art, modifications to one's chimney would also be required.
A third example of a pre-heating device which attempts to reduce the operating costs of a hot water heating system is disclosed in U.S. Pat. No. 4,671,253 to Blount Sr. The apparatus disclosed therein includes a system of piping which directs the flow of incoming cold water through the attic of a residence prior to entering a hot water heater. Similar to the chimney exhaust pre-heater described above, this system may increase the overall heating efficiency of a building (heating water and air) by recycling otherwise wasted energy i.e. heat energy trapped in one's attic. Again, this would be dependent upon the increase in total efficiency when compared to the efficiency of heating water and air alone. If, however, the additional energy is provided from a cost free source (eg. climate), a reduction in the total heating costs may be realized. The system described in Blount Sr., however, has at least two major disadvantages. First, similar to the aforementioned pre-heating devices, this system requires extensive modification to one's existing hot water system. These modifications include, among other things, constructing a complex system of piping to divert cold water through one's attic. As will be apparent to one skilled in the art, such modifications may also require additional pumping means, depending on the location of one's hot water heater, in order to overcome any potential energy increase associated with increasing the elevation of the water. Second, as attics are typically uninsulated, such a system is effective during warm seasons only. Furthermore, the system's pipes are prone to breakage by freezing due to exposure of the pipes to cold air in the attic. In that respect, multiple valves are necessary, and are in fact required in the system described in Blount, Sr., to divert the water away from the heat exchanger in winter months. Thus, the effectiveness of this device is limited and largely climate dependant.
A need exists, therefore, for an improved method and system of pre-heating water for hot water heaters.